I read a post elsewhere that claimed H4350 was definitely temperature sensitive. It really made me wonder what others have found.
Quite a few years ago I started using certain powders exclusively because I do most of my testing in the heat of the summer and most of my hunting in 30 degree or less temps. I use Varget, RL-15 and H4350 and have never noticed a problem with any of these. Maybe because when I'm hunting I'm not always able to detect any change?
Whats your personal experience with the temperature insensitive powders?

I've used both Varget and H4350 in very cold weather, using loads developed during warmer months. I've had no reason to think they were significantly affected by the temperature, but then I haven't shot any elk over a chrony either. I'm worried that they wouldn't sit still long enough for me to set it up

Up until that was mentioned on another thread, I've never heard of H4350 being temperature sensitive either. I've heard in the past that IMR 4350 was a little temp sensitive, but like I stated on my reply to that, I load H4350 exclusively in my .270 win for two different bullets and I cant say I've had any problems with H4350.

All powders are temperature sensitive. When a round's powder charge gets hot, it'll shoot bullets out faster and with a bit higher pressure. The opposite happens when powder's very cold. Some are more sensitive than others.

Primers are also temperature sensitive.

All of which is why SAAMI has temperature specs for qualifying ammo's velocity and pressure.

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http://www.accuratepowder.com/faq/
"7. What is the real story behind temperature stability?
Most of our powders are not insensitive, and will show some effect at hot and cold temperatures.

However, we test at -40F and +125F and the deviation in most cases are ca 3% to 5% at these extreme levels. Therefore most shooters do not notice much difference under normal practical hunting conditions."

Maybe so to some extent Bart, but the variations in velocities have to be minor, at least not effecting my deer hunt or my coyote shooting, in my neck of the woods actuall temps vary from 20> 45 degrees, I haven't noticed any problems in cold temps or hot temps. Be it the only hot temps I shoot in are at the range, usually during the summer, but I relegate my duties elsewhere when it's too hot.
When it all comes down to it what group of shooters will notice any variations due to hot vs cold temps?

H4350 and Varget are both in Hodgdon's Extreme powder line that is marketed as being less temperature sensitive than most others. It's one of the reasons I use them for hunting ammunition.

I have experienced with some powders increased pressure during very hot weather, really flattening primers with a near max load that I had tested early in the spring with no such issues. It definitely can be a factor, and some spherical powders are known to be more difficult to light off in very cold weather, often prompting a recommendation for magnum primers. But for the most part I don't think low temp is going to cause 30% loss of power or anything close to that. I'm thinking maybe a couple hundred FPS at most - but again I haven't chronoed anything that cold either.

I was the one who made the statement in the other thread that caused this thread to spin off. I am not saying that H4350 will change 2 minutes of impact. What I am saying is that its velocity will vary with temperature change despite what Hodgdon or anyone else says. It would be accurate to say it is less temperature sensitive than IMR, but it is a total misstatement to say it is immune to temperature changes, because it is not. To be honest, I have never known Hodgdon to claim it was not temperature sensitive.

the load density is also going to figure into the temperature sensitivity, or lack thereof, of any given powder.

this is why you see some folks claiming that powder "X" is temp stable, and others say that that same powder "X" is not temp stable--they're using them in different cartridges and/or different load densities.

Years ago I used IMR3031 with my 45-70. It went BOOM in the cold morning and BOOM in the warm afternoon. 3031 was showing almost 100fps velocity difference over temp, according to my Chrony - which didn't matter for 100yd shots but was audibly noticeable. Later I switched to H4198, part of the "extreme series". Now it goes BANG morning, noon, night, summer and winter.

Burning is a chemical reaction and all chemical reactions are susceptable to ambient temperature. The end temp of gun powder burn is probably largely independant of external temp variations but the powder temp at ignition will surely have an impact on the intitial burn rate and, from that, the peak pressure.

Some powders are less sensitive to normal temp changes but none are or can be totally insensitive to the ambient temperture.

Never really noticed much change with 4350 in my .260 Rem doing sets of 20 rounds in 20 minutes with a heavy barrel but I do know that is not a good idea with RL10x in a .204 to let the round sit in that hot chamber for more than a few seconds it makes for some screwy chrono results. Saw the speed jump up 150 fps for same load and mild cratering on the primer, tried it a second time and same thing

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Somewhere around here I have a picture of primers in 6 spent .44mag cases. They were all shot from the same gun outta the same batch I reloaded using a near max load of H110/W296 under a 240JHP. Only difference was 2 each were shot @ 90+ degrees, 70 degrees and minus 5 degrees. While reading primers is no indication of pressure, it's very obvious by the looks of those primers, that there was a good deal of difference in pressure between the three different temps.

I'm sure someone somewhere can debunk this, but if it were brass monkey cold outside, wouldn't the barrel steel contract some, rendering the bore a little smaller in diameter, and wouldn't that smaller bore diameter somewhat affect velocities? Conversely if it were blazing hot, wouldn't the bore diameter be somewhat larger, thus affecting velocities of ammunition fired from that same firearm?

I guess I wonder whether powder temperature is the only variable.

Or stated otherwise, even if you had a cartridge inside your jacket, taped inside the armpit or something so it was nearly 100 degrees f., and then placed that cartridge in a chamber of a negative 40 degrees rifle, and fire it quickly, would it still perform as it would if ambient temps were 100 degrees f.?

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